Characteristics required of optical receivers in general include high receiver sensitivity, wide dynamic range and high response speed. In order to achieve wide dynamic range, which is one of the required characteristics, a variable optical attenuator is widely used. PTL (patent literature) 1 describes an example of optical receiver that controls a variable optical attenuator by feedback control.
The optical receiver described in PTL 1 includes the variable optical attenuator on the light input side of an APD (avalanche photodiode). When the level of an output signal from the APD exceeds a given value during reception of a burst optical signal, the attenuation of the variable optical attenuator changes from low to high. When the reception of the burst optical signal ends, the attenuation of the variable optical attenuator changes from high to low. PTL 1 states that such a configuration can achieve a high receiver sensitivity and wide dynamic range and can prevent adverse effects of on burst light reception in which the ratio between the time during which an optical signal is received and the time during which an optical signal is not received is extremely large. PTL 2 and PTL 3 describe optical receivers including variable optical attenuators.